A driving assistance system which installs an equipped camera backward in a rear trunk portion or the like of a vehicle and provides an image of a rear side of the vehicle picked up by the equipped camera to the driver is spreading nowadays. Some of the driving assistance systems translates/synthesizes a real image picked up the equipped camera into an image that looks as if such image is picked up from a viewpoint being set virtually and displays a resultant image on a monitor, and the driving assistance systems are mainly used for the purpose of the safety check and the parking assistance in backing the vehicle.
As a three-dimensional projection model used to synthesize/translate the image, for example, as shown in FIG. 10, a three-dimensional projection model 100 configured to have a cylindrical surface model 101 and a flat surface model 102 is used. Then, a real image picked up by a real camera 103 is translated/synthesized into an image viewed from a virtual camera 104, and then is displayed as an image projected onto the three-dimensional projection model 100 on an equipped monitor.
FIG. 11 is an explanatory view showing an image obtained by projecting a straight line 105 shown in FIG. 10 onto the three-dimensional projection model 100. A straight line image 105a on a monitor screen 106 is displayed to be folded at a model boundary 107 between the cylindrical surface model 101 and the flat surface model 102. In this manner, the reason for that originally straight line 105 is translated as a folded image 105a when the three-dimensional projection model 100 configured to combine the cylindrical surface onto which the far image is projected and the flat surface onto which the near image is projected is used is that distortion of the display is concentrated onto the model boundary 107 between two three-dimensional projection models 101, 102. Thus, when the driver looks at this folded image 105a, he or she perceives a sense of incompatibility.
Therefore, if two three-dimensional projection models are smoothly connected by a curved surface (third three-dimensional projection model), the straight line image 105a is smoothly curved, as shown in FIG. 12, and it is possible to relax the sense of incompatibility. However, since the distortion is concentrated onto a projection surface 108 onto the third three-dimensional projection model, a sense of incompatibility still remains.
Therefore, in the prior art set forth in JP-A-2002-83285, for example, the three-dimensional projection model shown in FIG. 13 is proposed. This three-dimensional projection model 200 is configured to have the cylindrical surface 101 onto which the far image is projected, and a spherical surface model 201 which is successively connected to this surface and onto which the near image is projected. In this manner, since the spherical surface model 201 is used as the model on which the picked-up image near the vehicle is projected, an overall projected image on the spherical surface model 201 changes smoothly and therefore a sense of incompatibility of the driver can be considerably relaxed.
However, if the above three-dimensional projection model 200 shown in FIG. 13 is used, the picked-up image near the vehicle is never distorted at the particular portion concentrated, but it occurs a problem that the distortion is generated in the overall image. For example, the image obtained by picking up an image of a lattice pattern on the ground 202 by the real camera 103 and then projecting the picked-up image onto the spherical surface model 201 is distorted as a whole, as shown in FIG. 14. That is, there is a problem such that a group of straight lines constituting originally a lattice on the ground 202 are displayed as a group of curved lines on the screen 106, and it is difficult to grasp positional relationships between the driver's own vehicle and the surroundings based on such image.
An object of the present invention is to provide a driving assistance system in which a three-dimensional projection model capable of monitoring/displaying a surrounding image of a vehicle as a less distorted image while suppressing incompatibility with a distant image from the vehicle is installed.